Modern internal combustion engines, such as turbo charged diesel engines are the subject of stringent emission requirements. One characteristic that features in such requirements is the amount of particulates or visible smoke that an engine emits during running. Many factors influence the amount of particulates that an engine may emit such as fuel quality, operating environment and engine characteristics such as air-to-fuel ratio, speed, load and transient behaviour. One particular reason of smoke generation may be the lack of sufficient combustion air charge during aggressive transient states. One example of such transient state may be a rapid demand for the increase of power output of the engine by an operator who decides to increase the engine speed from idle to full speed by suddenly depressing the accelerator pedal fully. Since the engine accelerates in a delayed fashion, for a short time too much fuel is injected in relation to the amount of air available for combustion, which causes an incomplete combustion and possibly a drop in temperature in the combustion chamber and hence an excessive smoke development. Significant reduction of visible smoke emitted by turbocharged diesel engines upon acceleration has been achieved over the years by pressure sensitive devices such as aneroid controllers. Aneroid controllers influence the amount of fuel delivered to the injected system depending on the inlet manifold or boost pressure.
U.S. Pat. No. 4,727,839 describes such an aneroid controller. The controller as disclosed describes a multi-spring control arrangement to attain an improved fuel regulating characteristic rather than just a standard performance characteristic. Although the controller is compact and allegedly provides an improved regulating characteristic over the prior art, the design is complicated and may be prone to failure. The system is based on a spring loaded diaphragm having a mechanical arrangement attached for actuating a mechanism in a fuel injection pump. The diaphragm is being actuated under the influence of intake air pressure. The forces generated by the pressurized intake air are fairly weak and the system connected to the diaphragm balancing the gas forces must therefore not offer much resistance. A light spring arrangement is therefore preferred which may also improve the responsiveness of the system in general. Furthermore, as the controller is a “dry” controller, a sealing arrangement has to be in place to prevent any fuel from traveling up from the fuel injection pump into the controller. Normal tear and wear of the system in combination with the resistance offered by the sealing arrangement may hinder a proper operation of the controller.
The current disclosure is aimed at improving or overcoming at least some of the aforementioned disadvantages.